There has been sporadic interest in cement concrete as electrical insulators since about 1952. Recently, this interest has quickened due to mainly to economic pressures brought about by the rise in cost of conventional porcelain and epoxy insulators.
A major problem in the use of concrete as an electrical insulator is the difficulty in constructing an insulator which has sufficient resistance to high humidity. Concrete is a mixture of an aggregate and a binder which can be cement or a polymer, or both. All polymers shrink to some extent when they are cured. Accordingly, when the polymer in a polymer containing concrete is cured, capillaries inevitably are formed and these capillaries permit atmospheric moisture access to the interior of the insulator body. Moisture is the single most deleterious component which affects the electrical properties of a polymer containing concrete. A seemingly insignificant amount of residual moisture, i.e., about 0.2% or less, can adversely affect the electrical properties.
In addition to allowing moisture access to the interior of the concrete insulator, the capillaries also allow air access to the interior of the insulator and facilitates the interconnection of electrically conducting air pockets. This is obviously undesirable.
A method has now been discovered which permits the adverse effect of the capillaries being formed during polymer curing to be overcome and additionally increases the mechanical strength of the insulator. The method involves the filling of the capillaries as they are being formed and additionally provides a sealant coating on the surface of the insulator.
It is the object of this invention to prepare a polymer containing electrical grade concrete in which the capillaries normally formed during polymer curing and their effect are largely overcome and the mechanical strength of the insulator body is improved. This and other objects of the invention will become apparent to those skilled in the art from the following detailed description.